1. Technical Field
This invention relates to a method of passivating at least a portion of a surface of a stainless steel member so as to retard the buildup of radioactive material on such a surface portion, and to the use of the passivated member in the water system of a light water type nuclear reactor. More particularly, the invention relates to a method of passivating stainless steel pipe which is utilized in the water system of a light water type nuclear reactor.
2. Background Art
When light water nuclear reactors, which term includes both pressurized water and boiling water reactors, have been in use for some time, radioactive products build up on the inner walls of the piping of the water system. Basically, precursors of radioactive materials such as Co.sup.60, Zn.sup.65, Co.sup.58, are leached from pipes and the radioactive materials are formed from the precursors in the flux zone of the nuclear reactor and then are transferred through the water to other portions of the system where they collect on the inside of the piping. As a result, maintenance personnel who must work on the pipes of the light water system are exposed to the generated radiation field.
One attempt to alleviate the above set out problem has been to shut down the reactor once the radioactivity on the pipes of the reactor have become too radioactive and then to take out these pipes and either decontaminate or (if the structural integrity of the pipe has become inadequate) replace them with new pipes. Unfortunately, the radioactivity level builds up very quickly after such processes since the water is already saturated with dissolved radioactive materials and since such materials can quickly become incorporated into the surfaces of the replacement pipes.
Attempts to solve the latter problem, that of the much faster buildup of radioactive materials on replacement pipes than occur on original or new equipment, have consisted of trying to prepassivate the replacement pipes in a liquid system much like that to which they are to be exposed when installed in the water systems of light water reactors. Unfortunately, the passivation obtained has not been nearly sufficient to stop the rapid buildup of radioactive materials on the surfaces of the decontaminated or replacement pipes. Furthermore, it is relatively expensive to form a closed system to accomplish such passivation as has been attainable in the past.